Conference Paper

Design and development of a novel control regime for microgenerating wind turbines

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Straightforward analysis can show that it is difficult to implement a successful electrodynamic braking system for a small wind turbine system, i.e. of swept area less than 200 m2 and power rating of 50 kW. Two principal difficulties are: (i) the peak short-circuit torque of the electrical generator can be far too low to overcome the torques associated with the wind turbine rotor, even at wind speeds close to rated; (ii) the energy dumped into the generator during braking is significant and can cause swift heating to high temperatures. Transient electrical effects can also lead to electrical and electronic component failures. Documented failures in machines of up to 10 kW indicate that it is the case that electrodynamic braking is not well understood throughout the industry. Additionally, the academic literature on the topic is sparse. In this paper, we show how very straightforward analysis can shed light on the edge cases for electrodynamic brake systems and help to avoid expensive errors.
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A magnetic brake system was fabricated for use with small wind turbines. The torque of the pivot did not change as the speed of revolution increased when the magnetic array disc was far from the salient of the alu-minum housing, the torque abruptly increased as the magnetic array approached the salient of the aluminum housing. The torque increased as a quadratic function of the speed of revolution when the distance between the magnetic array and the datum point was 60 mm.
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Renewable wind resources in UK urban areas are analysed in this paper based on the available wind speed measurements and wind turbine manufacturers' data. Power curves of selected wind turbines and measured/fitted wind speed distributions for considered UK urban sites are used for the estimation of wind turbines maximum annual energy outputs. These results are then compared with the energy outputs obtained when commonly assumed UK mean wind speed values and Rayleigh distribution of average wind speeds are used instead of the measurements. The paper concludes that standard assumptions for UK mean wind speeds and Rayleigh distribution cannot be used for the correct assessment of UK urban wind resources, while Weibull distribution can be used if corresponding factors k and λ are determined from the measured wind speed data.
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In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.
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The purpose of this paper is the application of some existing techniques for the modelling and regulation of an eddy current brake process. An approximate theoretical model is derived for the behavior of an eddy current disc brake in the low-speed zone. Input-output information is used to obtain a polynomial state-affine behavior model for such a process. Dynamic and static feedback compensator schemes are proposed for the process speed control in the presence of unknown braking resistant torque. The dragging torque value is estimated by an appropriate nonlinear observer. Experimental results are presented.
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The output power of present wind turbines is continuously increasing. At high power levels, to limit mechanical stresses and power surges in the grid it is necessary to use speed control systems. The double-output induction generator (DOIG) system is an excellent solution to adjust the speed over a wide range. At present the two converters associated with the DOIG use high power IGBTs with medium switching frequencies in order to optimise the current waveform in the generator and in the grid. The two converters need a high performance control system operating with high sampling frequencies and complex control algorithms. The voltage source IGBT converter connected to the grid controls the active and reactive power supplied and imposes a low level of harmonic distortion. This paper presents the results obtained with such a system.
A theoretical model ss derived for eddy current disc brakes with iron pole shoes with a wide spacing. The eddy current in the disc is not a simple periodic function allowing representation by sine functions. In the high speed region, the current distribution around the polo shoe occupies a limited zone width proportional to the air gap. The theory based on this effect leads to reasonably accurate values of the critical torque and speed compared with experimental data. The predicted air gap dependency of the critical values agrees better with experimental results than Rudenberg's theory
Design,Operation and Diagnostics of a Vertical Axis Wind Turbine
  • G Colley
Wind turbine generator having an eddy current brake, wind turbine having such a generator, and associated methods
  • mongeau